Tom Buck on fri 19 dec 97
Suzanne S:
1) C5 is 1200 C, 2200 F, quite high, no? 2) Copper carbonate basic
(the green powder) soon becomes Copper oxide black (CuO) in a firing (at
200 C) and CuO (if not functioning as a flux oxide) will persist as a
solid until 1300+ C. But like all solids/liquids, at a lower temperature,
some molecules of CuO will acquire more energy (vibration) than others and
thereby move into the gaseous state. So, quite a few CuO molecules will
migrate at 1200 C to the gases in the kiln and, if the kiln is not
ventilated, some of these CuO molecules will bump into nearby pots, will
be "cooled" slightly and condense on the pot's surface. Hence, the green
blush.
3) How to enhance this effect? If I wanted to try to achieve this
copper vapour coating on my pots, I would place a thin layer of copper
carb in a shallow unglazed bowl in the kiln's hot spot, and fire as usual
but likely with a 20-30 minute soak at full cone 5 (or close to that). I'd
also use a white body + clear glaze or a white glaze on my pots so the
green blush would show to best effect... it would probably be lost on a
blue- or brown-glazed pot.
Tom Buck ) tel: 905-389-2339
& snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).
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